We have been investigating nucleic acid structure involved in the control of transcriptional initiation, termination, and post-transcriptional processing and modification of various RNA transcription products. Nucleic acid sequences have been determined in the 3'-terminal regions of a number of bacterial RNA polymerase mediated transcription products synthesized from lambda and lambda gal transducing phages. We have also examined nucleic acid structure in the "terminator" regions of the DNA template beyond the 3'-ends of several RNA transcription products. We are presently defining the structure surrounding an RNA polymerase stop-signal in bacteriophage lambda which is totally dependent on the protein termination factor, rho, for its function. Nucleic acid structure in the regulatory region of the galactose operon of E. coli has also been examined. In addition, the nucleotide sequence of a region of the bacteriophage T7 genome which lies between two adjacent "early" messenger RNAs has been completed. This intercistronic region contains all of the structural information necessary for specifying the processing event (i.e., cleavage by the host encoded endonuclease RNase III) which matures this polycistronic precursor RNA into individual monocistronic mRNAs.